i6o THE STORY OF THE BIRDS 



resident in our Islands, but, as every ornithologist 

 knows, vast numbers of migrant Goldcrests ap- 

 pear in them in autumn. The Hooded Crow is 

 a resident in Scotland, but in many parts of the 

 Continent it is a migrant, crossing the North Sea 

 in vast hordes every autumn to winter with us. 

 Similarly in the south we find certain migratory 

 species, some individuals of which appear to be 

 sedentary, such, for instance, as the Sedge 

 Warbler, the Chiffchaff, and the Corncrake. 

 Not only, however, is the habit of migration 

 irregular, but the distance traversed is very vari- 

 able among the individuals of a species, some 

 journeying more than double the distance that 

 others do. The breeding range of the Wheatear, 

 for instance, extends from North Africa to Jan 

 Mayen, whilst the winter or range base of this 

 species extends to the Equator. 



A few words now as to the Cause of migration. 

 Perhaps the most popular opinion respecting this 

 is, that the habit is due to failure of food. Migra- 

 tory birds leave their winter quarters or base as 

 summer comes on, and the requisite food begins 

 to fail ; whilst they quit their northern haunts as 

 winter approaches, for a similar reason. Many 

 naturalists of eminence are content to find 

 the cause of migration in these suppositions. 



